Compact fluid actuator and method of making it

ABSTRACT

A compact fluid powered actuator is constructed from a flexible tube assembled over a rigid core. The actuator includes an expansible chamber formed between the tube and the core. The chamber is bounded by naturally efficient and lowly stressed seals at the ends of the tube which tightly match the periphery of the core. This construction lends itself to mass production methods wherein a long core is assembled with a long tube enabling a plurality of actuators to be manufactured simultaneously.

United States Patent Steger Nov. 28, 1972 COIVIPACT FLUID ACTUATOR AND3,304,386 2/ 1967 Shlesinger ..200/83 METHOD OF MAKING IT 2,676,6094/1954 Pfarrer ..92/92 3 006 306 10/ 1961 Pfeifier et a1. ..92/92 I [72]memo Dmm'd J stege" Cmmth Ky 3,051,143 8/1962 Nee ..92/92 [73] Assignee:International Business Machines Corporation, Armonk, PrimaryExaminer-Edgar W. Geoghegan 22 Filed: Dec. 16, 1970 f Attorney-Hamlinand Jancm and E. Ronald Coffman [21] Appl. No.: 98,775

[ ABSTRACT [52] US. Cl ..92/92, 92/91 A compact fluid powered actuatoris constructed f [51] Int. Cl ..Folb 19/00 a flexible tube assembledover a rigid core The actua [58] Fleld of Search ..92/91, 92 tor incudesan expansible chamber formed between the tube and the core. The chamberis bounded by [56] References and naturally efficient and lowly stressedseals at the ends UNITED STATES PATENTS of the tube which tightly matchthe periphery of the core. This construction lends itself to massproduction 2,612,909 lO/l952 Keller ..92/92 methods wherein a long corei assembled with a long 2,048,771 7/1936 Baldwin ..92/92 tube enabling aplurality f actuators to be manufac 2,991,763 7/1961 Marette ..121/48med simultaneously 3,016,884 1/l962 Merriman ..121/48 3,048,121 8/1962Sheesley 103/152 10 Claims, 8 Drawing Figures PATENTEUWZB SHEEI 1 OF 23103-853 FIG. 1

FIG. 2

FIG. 3

INVENTOR DONALD J. STEGER ATTORNEY COMPACT FLUID ACTUATOR AND METHOD OFMAKING IT BACKGROUND OF THE INVENTION Bellows, pistons and diaphragmshave long been employed as expansible chamber actuators for convertingpneumatic or hydraulic energy into an output force. A typical limitationon the use of actuators has been the cost and complexity of overcoming,or of living with, the problems of fluid sealing and in the case of abe]- lows or diaphragm, fracture of a flexible member.

Of these three traditional actuators, the bellows provides the greatestsimplicity since it can be manufactured somewhat as a single member. Thetraditional bellows includes a plurality of so-called accordion pleatswhich enable a significant output stroke. The apex of each pleat has asmall radius bend which is subject to failure upon repeated stressing.The bellows device, while mechanically simple due to its potential onepiece construction, is rather complex from a manufacturing viewpointparticularly where small size bellows are concerned. In small sizebellows the uniformity of wall thickness will determine the reliabilityof the bellows over a long period of time. Those skilled in the artfamiliar with the techniques for molding thin complex walls of flexiblematerial and maintaining uniform wall thickness can recognize thelimitations of the bellows actuator.

My invention employs the readily manufacturable shapes of a rigidcylinder and a flexible tube to minimize the sealing and flexure problemof an expansible chamber in a simple and highly effective manner. A tubepress-fit over a cylinder of substantially equal periphery forms anatural or inherent seal which can be easily supplemented by a heat bondif desired. The reaction and support functions necessary to the actuatorare compactly provided by the internal rigid core which lends itself toa simple snap-in frame mounting like that common to some fuses ofsimilar shape. While the construction of the tube can be varied to someextent, I prefer to employ a relatively non-elastic material that ispre-formed into a bulge or extended surface portion defining theexpansible chamber. Actuation of the device thus involves only flexuraldeformation rather than any significant amount of stretching. Due to thesurrounding relationship of the tube with the cylindrical core, it ispossible to restrict flexure to relatively large radii of curvature andthereby minimize the tendency for local failure that limits thepotential success of a bellows type device.

While the actuator that l have invented has the capabilities indicatedabove which by themselves make it a desirable and highly effectivedevice, it should be apparent that the simple shapes of tubes andcylinders can be manufactured to relatively close tolerances. Uniformwall thickness of a tube is relatively easy to obtain. Such uniformityis required to minimize stress concentrations that could cause localizedfailure. My actuator also lends itself to large quantity manufacture tominimize its basic cost. The fundamental shapes of a cylinder and a tubeenable simultaneous construction of a plurality of expansible chamberson a long rod surrounded by a long tube. These devices can later besevered into a plurality.

These and other concepts, features, and advantages of my fluid actuatorand the method of making it will be apparent to those skilled in the artfrom reading and understanding the following more specific illustrativeembodiment of my invention wherein reference is made to the accompanyingdrawings, of which:

FIG. 1 is a perspective view of a fluid actuator constructed inaccordance with my invention;

FIG. 2 is a longitudinal cross-sectional view of the actuator shown inFIG. 1 and taken along lines II II of FIG. 1;

FIG. 3 is a lateral or end cross-sectional view of the actuator shown inFIG. 1 taken along lines III III thereof;

FIG. 4 is a perspective view of the cylindrical core component of theactuator shown in FIG. 1;

FIG. 5 is a perspective view of the tubular component of the actuatorshown in FIG. 1;

FIG. 6 is a somewhat schematic view showing a method of making thecylindrical core component of an actuator in accordance with myinvention;

FIG. 7 is a schematic view showing a preferred method of forming thetubular component after assembly with the core component in accordancewith my invention and FIG. 8 is a schematic manufacturing view showingthe separation of a plurality of simultaneously formed devices intoindividual devices.

Referring now more specifically to the drawings, in FIGS. 1, 2, and 3there is shown a compact fluid powered actuator or device 10 comprisinga substantially rigid elongated core member 20 that is best seen in FIG.4. Core member 20 is surrounded by a flexible relatively non-elastic,fluid impervious. tubular membrane or tube 30 that is best seen in FIG.5. The tube 30 has a tubular axis 35 which is aligned with the axis 29of the core member 20 when the two are assembled. The tube 30 includesan extended surface on bulge portion 31 that overlies an intermediatelypositioned recessed section 21 of the core member 20 to form aninflatable or expansible chamber 32. Fluid for inflating chamber 32 issupplied through a suitable conduit 1 l'within the core member 20. Thefluid is transmitted through an inlet 22 and a longitudinal bore 23 toan elongated channel portion 23a where it is applied internally to thetube 30 to cause inflation of the chamber 32. Due to the inelasticcharacter of tube 30, bulge portion 31 defines a fixed maximum volumefor chamber 32 when inflated as shown in broken lines in FIG. 2.

An output or reaction member 40 is movably supported by a pivot axis orshaft 41 connected to a mounting bracket 42. As shown in broken lines inFIG. 2, output member 40 is driven upwardly upon inflation of thechamber 32. The mounting bracket 42 is secured to a frame part 43 by ascrew 44 and includes a pair of spaced spring clip portions 45 forsecurely receiving the ends of the core member 20. It will be seen thatupwardly turned portions 46 of the spring clip portions 45 willresiliently removably receive the core 20 in a manner similar to anelongated fuse mounting. Obviously other mounting devices can beemployed with equal facility.

The details of the core member 20 are better shown in FIG. 4. The coremember 20 is essentially of oblong cylindrical lateral cross-sectionalor peripherial configurationr This cross-section, which is substantiallyuniform at opposite end sections 24 that are enlarged with respect tothe recessed section 21; provides a flattened configuration havingopposed primary surface portions 25 that provide a relatively large areacompared to the side or secondary surface portions 26. The recessedsection 21 has a longitudinal extent 27 that is long relative to thewidth 28 of the core member 20 thereby providing a relatively largepotential surface area to lie in projection with the bulge portion 31 ofthe tube 30.

The recessed section 21 also has a surface configuration 21a that ismade substantially complementary to the shape of a force receivingportion 47 of the output member 40. As best seen in FIG. 2, the forcereceiving portion 47 thus snuggly fits against the extended surfaceportion 31 of the tube 30 and rests against the complementary configuredsurface 21a (see FIG. 3) of the recessed portion 21 to define a stableend limit or rest position. Only a single layer of uncrimped membrane ofthe tube 30 lies between the force receiving portion 47 and the surface21a, since as shown in FIG. 3, the excess material of the bulge portion31 moves outwardly to the side where it does not interfere with theprecise rest position of output member 40.

The core member 20 can be made of a variety of materials and byprocesses that include both molding and machining. If the core member 20is made from stock material including the longitudinal bore 23 whichextends throughout the entire length thereof, then a plug 23b must beprovided to seal one end of the bore 23.

The tube 30, as shown in FIG. 5, has an internal periphery that issubstantially equal to the external periphery of the core member endportions 24 to provide a tight fit therewith. It is preferable to employa relatively non-elastic, but thermoplastic material in constructing thetube 30 to enable the molding of bulge 31 after the tube 30 has beenmounted upon the core member 20. It will be recognized however thatadvantages remain even if an elastic membrane is employed without apre-formed bulge 31.

The tube 30 is assembled with the core member 20 by moving the tube 30along the longitudinal rectilinear axis of elongation 29 of the coremember 20 and is inherently sealed therewith by the interference betweenthe closely matching end portions 34 of the tube 30 and the end sections24 of the core member 20. This inherent seal can be supplemented bythermoplastic bonding at 33 through the use of a heated tool or anultrasonic device. Having assembled an inflatable device comprising thetube 30 mounted on the core member 20, the actuator is constructedsimply by plugging this device into the mounting bracket 42 shown inFIG. 1.

The fundamentally simple and compatable shapes of a cylindrical coremember and a tubular membrane enable efficient mass production of theseactuators. As shown in FIG. 6, an elongated rod of stock material 50provided with a longitudinally extending bore 51 is machined by acutting tool 60 to provide a plurality of spaced recesses 52 which areseparated by unmodified sections 53 therebetween. Having manufactured acore member with i a plurality of recessed sections 52 therein, athermoplastic tubular membrane 54 is forced thereon with somewhat of apress fit. This elongated assembly then is placed in a mold 61 as shownin FIG. 7 containing a plurality of mold cavities each having a surfaceconfiguration 62 that defines the desired inflated shape of the bulgeportion 31 (see FIGS. 2 and 5 Also the mold can contain heating devices63 for bonding the tube 54 to the core sections 53. The tubular membrane54 is heated prior to insertion in the mold to a temperature where it isthermoplastic. When the elongated heated assembly is placed in the mold61 the membrane 54 is stretched by inflation through either theapplication of pressure to the bore 51 or by drawing a vacuum in themold cavities 62. The stressed membrane thus permanently stretches to ashape defined by the mold cavity surface 62 and when colled will remainin this configuration. As shown in FIG. 8, the molded assembly isdivided into individual fluid devices 55 by a cutter 64 and later can befinally processed to the specific configuration desired as shown in FIG.1 for example.

Those skilled in the art will recognize that I have disclosed a uniquelysimple but effective fluid actuator concept which can be embodied in avariety of materials and manufactured in a variety of ways. While aspecific embodiment and a specific manufacturing method have beendisclosed to enable those skilled in the art to understand and practicemy invention, it is to be recognized that various modifications can bemade without departing from the inventive concepts I have disclosed.Accordingly these concepts are to be limited only by the specificlanguage of the appended claims.

I claim:

1. A compact fluid powered actuator comprising: a substantially rigidcore member extending along an axis of elongation and having first andsecond relatively enlarged end sections positioned along said axis andseparated by an intermediate recessed section and a bore that defines afluid inlet intersecting said recessed section,

a flexible, fluid impervious elongated tubular membrane oriented so thatits tubular axis extents along said core axis and passes through saidcore end sections, said membrane enveloping said core member at saidrecessed section and having first and second end portions that closelymatch and continuously sealingly encompass respective ones of said pairof opposed end sections to thereby define a substantially closedexpansible chamber connected with said fluid inlet,

a reaction member positioned adjacent said membrane at said recessedsection for receiving displacement force from said membrane uponintroduction of fluid to said chamber through to said fluid inlet, and

means mounting said core member and said reaction member for relativemovement therebetween.

2. An actuator as defined in claim 1 wherein said recessed sectiondefines a surface configuration, and wherein said reaction memberincludes a force receiving portion contacting said membrane and having asurface configuration that is substantially complementary to saidrecessed section defined surface configuration.

3. An actuator as defined in claim 1 wherein said membrane is made of arelatively non-elastic material and has, at the region thereof that.overlies said recessed section, an extended surface portion defining aninflatable chamber having a predetermined fixed maximum volume.

4. An actuator as defined in claim 2 wherein said membrane is made of arelatively non-elastic material and has, at the region thereof thatoverlies said recessed section, an extended surface portion defining aninflatable chamber having a predetermined fixed maximum volume.

5. An actuator as defined in claim 1 wherein said membrane contacts thesurface of said recessed section of said core member when fluid is notintroduced into said fluid inlet and wherein the improvement furthercomprises:

an elongated channel formed in the surface of said recessed section andbeing extended in the direction of said core axis, said channelremaining at all times out of contact with said membrane andcommunicating with said bore for applying fluid introduced to said fluidinlet to a substantial area of said membrane.

6. An actuator as defined in claim 3 wherein said extended surfaceportion of said membrane contacts the surface of said recessed sectionof said core member when fluid is not introduced into said fluid inletand wherein the improvement further comprises:

an elongated channel formed in the surface of said recessed section andbeing extended in the direction of said core axis, said channelremaining at all times out of contact with said membrane andcommunicating with said bore for applying fluid introduced to said fluidinlet to a substantial area of said membrane.

7. An actuator defined in claim 1 further comprising a mounting bracketattachable to a frame and means on said mounting bracket for removablyreceiving at least one of said end sections of said core member forsupporting said core member in a substantially fixed position.

8. A compact fluid powered actuator comprising:

a substantially rigid core member extending along a rectilinear axis ofelongation and having an oblong lateral cross-sectional configurationproviding a pair of opposed primary surface portions having asubstantially greater area than the remaining secondary surfaceportions, said core member further having a recessed section formed inone of said primary surface portions intermediate a pair of relativelyenlarged opposed end sections, said recessed section being of alongitudinal extent that is substantially greater than its lateralextent, said core member further having a bore that defines a fluidinlet extending through one of said end sections and intersecting saidrecessed section,

flexible fluid impervious relatively non-elastic membrane having anextended surface position enveloping said core member at said recessedsection to define an inflatable chamber having a predetermined fixedmaximum volume, said membrane being sealingly received by each of saidend sections, and

reaction member positioned adjacent said membrane at said recessedsection for receiving displacement force from said membrane uponintroduction of fluid to said fluid inlet, and

means mounting said core member and said reaction member for relativemovement therebetween. 9. An actuator as defined 1n claim 8 wherein saidrecessed section defines a surface configuration, and wherein saidreaction member includes a force receiving portion contacting saidmembrane and being shaped to be substantially complementary to saidrecessed section defined surface configuration.

10. An actuator as defined in claim 8 wherein said membrane contacts thesurface of said recessed section of said core member when fluid is notintroduced into said fluid inlet and wherein the improvement furthercomprises:

an elongated channel formed in the surface of said recessed section andbeing extended in the direction of said axis, said channel remaining atall times out of contact with said membrane and communicating with saidbore for applying fluid introduced to said fluid inlet to a substantialarea of said membrane.

1. A compact fluid powered actuator comprising: a substantially rigidcore member extending along an axis of elongation and having first andsecond relatively enlarged end sections positioned along said axis andseparated by an intermediate recessed section and a bore that defines afluid inlet intersecting said recessed section, a flexible, fluidimpervious elongated tubular membrane oriented so that its tubular axisextents along said core axis and passes through said core end sections,said membrane enveloping said core member at said recessed section andhaving first and second end portions that closely match and continuouslysealingly encompass respective ones of said pair of opposed end sectionsto thereby define a substantially closed expansible chamber connectedwith said fluid inlet, a reaction member positioned adjacent saidmembrane at said recessed section for receiving displacement force fromsaid membrane upon introduction of fluid to said chamber through to saidfluid inlet, and means mounting said core member and said reactionmember for relative movement therebetween.
 2. An actuator as defined inclaim 1 wherein said recessed section defines a surface configuration,and wherein said reaction member includes a force receiving portioncontacting said membrane and having a surface configuration that issubstantially complementary to said recessed section defined surfaceconfiguration.
 3. An actuator as defined in claim 1 wherein saidmembrane is made of a relatively non-elastic material and has, at theregion thereof that overlies said recessed section, an extended surfaceportion defining an inflatable chamber having a predetermined fixedmaximum volume.
 4. An actuator as defined in claim 2 wherein saidmembrane is made of a relatively non-elastic material and has, at theregion thereof that overlies said recessed section, an extended surfaceportion defining an inflatable chamber having a predetermined fixedmaximum volume.
 5. An actuator as defined in claim 1 wherein saidmembrane contacts the surface of said recessed section of said coremember when fluid is not introduced into said fluid inlet and whereinthe improvement further comprises: an elongated channel formed in thesurface of said recessed section and being extended in the direction ofsaid core axis, said channel remaining at all times out of contact withsaid membrane and communicating with said bore for applying fluidintroduced to said fluid inlet to a substantial area of said membrane.6. An actuator as defined in claim 3 wherein said extended surfaceportion of said membrane contacts the surface of said recessed sectionof said core member when fluid is not introduced into said fluid inletand wherein the improvement further comprises: an elongated channelformed in the surface of said recessed section and being extended in thedirection of said core axis, said channel remaining at all times out ofcontact with said membrane and communicating with said bore for applyingfluid introduced to said fluid inlet to a substantial area of saidmembrane.
 7. An actuator defined in claim 1 further comprising amounting bracket attachable to a frame and means on said mountingbracket for removably receiving at least one of said end sections ofsaid core member for supporting said cOre member in a substantiallyfixed position.
 8. A compact fluid powered actuator comprising: asubstantially rigid core member extending along a rectilinear axis ofelongation and having an oblong lateral cross-sectional configurationproviding a pair of opposed primary surface portions having asubstantially greater area than the remaining secondary surfaceportions, said core member further having a recessed section formed inone of said primary surface portions intermediate a pair of relativelyenlarged opposed end sections, said recessed section being of alongitudinal extent that is substantially greater than its lateralextent, said core member further having a bore that defines a fluidinlet extending through one of said end sections and intersecting saidrecessed section, a flexible fluid impervious relatively non-elasticmembrane having an extended surface position enveloping said core memberat said recessed section to define an inflatable chamber having apredetermined fixed maximum volume, said membrane being sealinglyreceived by each of said end sections, and a reaction member positionedadjacent said membrane at said recessed section for receivingdisplacement force from said membrane upon introduction of fluid to saidfluid inlet, and means mounting said core member and said reactionmember for relative movement therebetween.
 9. An actuator as defined inclaim 8 wherein said recessed section defines a surface configuration,and wherein said reaction member includes a force receiving portioncontacting said membrane and being shaped to be substantiallycomplementary to said recessed section defined surface configuration.10. An actuator as defined in claim 8 wherein said membrane contacts thesurface of said recessed section of said core member when fluid is notintroduced into said fluid inlet and wherein the improvement furthercomprises: an elongated channel formed in the surface of said recessedsection and being extended in the direction of said axis, said channelremaining at all times out of contact with said membrane andcommunicating with said bore for applying fluid introduced to said fluidinlet to a substantial area of said membrane.